| 1. |
- Alqaysi, Hiba, et al.
(författare)
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Design Exploration of Multi-Camera Dome
- 2019
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Ingår i: ICDSC 2019 Proceedings of the 13th International Conference on Distributed Smart Cameras. - New York, NY : ACM Digital Library. - 9781450371896
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Konferensbidrag (refereegranskat)abstract
- Visual monitoring systems employ distributed smart cameras toeffectively cover a given area satisfying specific objectives. Thechoice of camera sensors and lenses and their deployment affectsdesign cost, accuracy of the monitoring system and the ability toposition objects within the monitored area. Design cost can bereduced by investigating deployment topology such as groupingcameras together to form a dome at a node and optimize it formonitoring constraints. The constraints may include coverage area,number of cameras that can be integrated in a node and pixelresolution at a given distance. This paper presents a method foroptimizing the design cost of multi-camera dome by analyzing tradeoffsbetween monitoring constraints. The proposed method can beused to reduce monitoring cost while fulfilling design objectives.Results show how to increase coverage area for a given cost byrelaxing requirements on design constraints. Multi-camera domescan be used in sky monitoring applications such as monitoring windparks and remote air-traffic control of airports where all-round fieldof view about a point is required to monitor.
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| 2. |
- Amir, Yousaf Muhammad, et al.
(författare)
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High Precision Laser Scanning of Metallic Surfaces
- 2017
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Ingår i: International Journal of Optics. - : Hindawi Limited. - 1687-9384 .- 1687-9392.
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Tidskriftsartikel (refereegranskat)abstract
- Speckle noise, dynamic range of light intensity, and spurious reflections are major challenges when laser scanners are used for 3D surface acquisition. In this work, a series of image processing operations, that is, Spatial Compound Imaging, High Dynamic Range Extension, Gray Level Transformation, and Most Similar Nearest Neighbor are proposed to overcome the challenges coming from the target surface. A prototype scanner for metallic surfaces is designed to explore combinations of these image processing operations. The main goal is to find the combination of operations thatwill lead to the highest possible robustness andmeasurement precision at the lowest possible computational load. Inspection of metallic tools where the surface of its edge must be measured at micrometer precision is our test case. Precision of heights measured without using the proposed image processing is firstly analyzed to be +/- 7.6 mu m at 68% confidence level. The best achieved height precision was +/- 4.2 mu m. This improvement comes at 24 times longer processing time and five times longer scanning time. Dynamic range extension of the image capture improves robustness since the numbers of saturated or underexposed pixels are substantially reduced. Using a high dynamic range (HDR) camera offers a compromise between processing time, robustness, and precision.
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| 3. |
- Fedorov, Igor, 1980-, et al.
(författare)
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Towards calibration of outdoor multi-camera visual monitoring system
- 2018
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Ingår i: ACM International Conference Proceeding Series. - New York, NY, US : ACM Digital Library. - 9781450365116
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Konferensbidrag (refereegranskat)abstract
- This paper proposes a method for calibrating of multi-camera systems where no natural reference points exist in the surrounding environment. Monitoring the air space at wind farms is our test case. The goal is to monitor the trajectories of flying birds to prevent them from colliding with rotor blades. Our camera calibration method is based on the observation of a portable artificial reference marker made out of a pulsed light source and a navigation satellite sensor module. The reference marker can determine and communicate its position in the world coordinate system at centimeter precision using navigartion sensors. Our results showed that simultaneous detection of the same marker in several cameras having overlapping field of views allowed us to determine the markers position in 3D world coordinate space with an accuracy of 3-4 cm. These experiments were made in the volume around a wind turbine at distances from cameras to marker within a range of 70 to 90 m.
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| 4. |
- Malik, Abdul Waheed, 1981-, et al.
(författare)
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Real Time Decoding of Color Symbol for Optical Positioning System
- 2015
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Ingår i: International Journal of Advanced Robotic Systems. - : SAGE Publications. - 1729-8806 .- 1729-8814. ; 12:5
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents the design and real-time decoding of a color symbol that can be used as a reference marker for optical navigation. The designed symbol has a circular shape and is printed on paper using two distinct colors. This pair of colors is selected based on the highest achievable signal to noise ratio. The symbol is designed to carry eight bit information. Real time decoding of this symbol is performed using a heterogeneous combination of Field Programmable Gate Array (FPGA) and a microcontroller. An image sensor having a resolution of 1600 by 1200 pixels is used to capture images of symbols in complex backgrounds. Dynamic image segmentation, component labeling and feature extraction was performed on the FPGA. The region of interest was further computed from the extracted features. Feature data belonging to the symbol was sent from the FPGA to the microcontroller. Image processing tasks are partitioned between the FPGA and microcontroller based on data intensity. Experiments were performed to verify the rotational independence of the symbols. The maximum distance between camera and symbol allowing for correct detection and decoding was analyzed. Experiments were also performed to analyze the number of generated image components and sub-pixel precision versus different light sources and intensities. The proposed hardware architecture can process up to 55 frames per second for accurate detection and decoding of symbols at two Megapixels resolution. The power consumption of the complete system is 342mw.
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| 5. |
- Nyström, Jonas, et al.
(författare)
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An experimental study of the chipping process with focus on energy consumption and chipping angles
- 2018
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Ingår i: Nordic Pulp & Paper Research Journal. - : Walter de Gruyter GmbH. - 0283-2631 .- 2000-0669. ; 33:3, s. 460-467
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Tidskriftsartikel (refereegranskat)abstract
- A series of chipping experiments were performed under both dynamic and quasi-static conditions in a laboratory wood chipper (dynamic) and in a MTS-servohydraulic testing machine (quasi-static). One aim with the experiments was to investigate the rate dependency of the energy consumption during chipping. Another aim was to try to determine the load per unit knife edge length required to initiate cutting. The experiments were carried out using different combinations of spout and edge angles. It was found that for large edge angles (keeping the spout angle constant at 30°) there was a slight rate dependency such that the energy consumption was larger at higher cutting rates which is quite in opposite of what is expected if wood is assumed to be a viscoelastic material. It was also found that to determine the force at initiation of cutting, is not a trivial task. Both Acoustic Emission monitoring and visual inspection was used to this end. The wood species used in this study was pine (Pinus silvestris).
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| 6. |
- Rydblom, Stefani Alita Leona, 1975-
(författare)
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Development and Test of an Imaging Instrument for Measurement of Water Droplets in Icing Conditions
- 2019
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Structural icing is a persistent challenge for the production of renewable energy from wind. It is mainly caused by supercooled atmospheric droplets of water, which are very common in cold climates. In the most exposed wind parks in Sweden, more than 10 per cent of annual energy production can be lost. Some properties of liquid water are included in current Numerical Weather Prediction (NWP) models and are used as input parameters for the estimation of icing, but they are rarely measured in-situ for verification or validation.To address this problem, a new instrument was developed.This compilation thesis is a collection of five articles describing the development, testing and verification of this instrument. Finally, icing and ice loads are measured and compared with a standard model and a model using Artificial Intelligence (AI) and empirical data.The new instrument, called Droplet Imaging Instrument(DII), is based on shadowgraph imaging using Light Emitting Diode (LED) light as background illumination and digital image processing. The components were selected with the possibility of low-cost volume production in mind. The applications of a commercial instrument based on this technique include, forexample, real-time in-situ icing condition measurements and assimilation and verification of data in NWP models. The instrument, alongside a reference instrument, was tested in two locations with different icing conditions. Shadowgraph imaging and its limitations as a measurement method for droplet size and concentration were investigated.The work presented shows that measurements of the size and concentration of water droplets using shadowgraph images can be used for the comparison and validation of NWP models and other instruments. The Coefficient of Variation (CV) for a given value of the concentration is lower than 1.6 % for droplets 25 µm in diameter, based on uncertainty in the size measurement only. The accuracy of the sampling volume can be improved by measuring the background light intensity in the position of the measured droplet.A fog chamber was used for initial tests. However, to evaluate models of ice accumulation, in-situ measurements are necessary. These measurements should use a temporal resolution of at least one sample per minute, preferably higher. With alimited amount of data, multivariate data analysis can be used to estimate the level of ice accretion. Together with a heuristic model of erosion/ablation, the resulting figures can be used to simulate the ice load.All of the instruments, as well as many other components used during the described field measurements, did at some point break due to the difficult weather conditions. An instrument for measurement of icing conditions needs to be designed with high environmental protection and endurance. The results in the attached papers may help and motivate further technical development of instruments that can measure atmospheric liquid water in icing conditions.
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| 7. |
- Rydblom, Staffan, 1975-, et al.
(författare)
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Field Study of LWC and MVD Using the Droplet Imaging Instrument
- 2019
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Ingår i: IEEE Transactions on Instrumentation and Measurement. - : IEEE. - 0018-9456 .- 1557-9662. ; 68:2, s. 614-622
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Tidskriftsartikel (refereegranskat)abstract
- The droplet imaging instrument (DII) is a new instrument for cost-effective in situ measurements of the size and concentration of water droplets. The droplet size distribution and the concentration of atmospheric liquid water are important for the prediction of icing on structures, such as wind turbines. To improve the predictions of icing, there is a need to explore cost-effective working solutions. Through imaging, a wide range of droplet sizes can be measured. This paper describes a study of the atmospheric liquid water content and the median volume diameter using the DII and a commercial reference instrument--the cloud droplet probe 2 from Droplet Measurement Technologies Inc. The measurement is done at a weather measurement station in mid-Sweden. For a second validation, the result is compared with predictions using a numerical weather prediction model. The size measurement of the DII is verified using polymer microspheres of four known size distributions. The study shows that the DII measurement is precise, but there is a systematic difference between the two compared instruments. It also shows that droplets larger than 50 μm in diameter are occasionally measured, which we believe is important for the prediction of icing.
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| 8. |
- Rydblom, Staffan, 1975-
(författare)
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Measuring Water Droplets to Detect Atmospheric Icing
- 2017
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis describes the exploration of a method to measurethe droplet size and the concentration of atmospheric liquid water. The purpose is to find a cost effective technique to detect the conditions for icing on structures.Icing caused by freezing atmospheric water can be a signifi- cant problem for infrastructure such as power lines, roads and air traffic. About one third of the global installed wind power capacity is located in cold climates, where icing of rotor blades is one of the major challenges.The icing process is complex and the result depends on a combination of the aerodynamic shape of the structure or airfoil, the velocity of the air and its contained water, the temperature, the mixing of snow and water, the concentration of liquid water and the Droplet Size Distribution (DSD).The measurement method is based on a shadowgraph imag- ing system using light emitting diode (LED) light as background illumination and digital image processing. A prototype instru- ment has been constructed. The components were selected keeping the possibility of low-cost volume production in mind. The applications of a commercial instrument based on this tech- nique are e.g. real-time in-situ icing condition measurements and assimilation and verification of data in numerical weather models.The work presented shows that measurements of the size and concentration of water droplets using shadowgraph images can be used for the comparison and validation of Numerical Weather Prediction (NWP) models and other instruments. The accuracy of the particle size measurement is high. The accuracy of the concentration measurement has the potential to become high due to the single-particle measurement range calibraiton. The precision of the instrument depends mainly on the number of images that is used to find each measurement value. The real-time performance of the instrument is limited by the image retrieval and processing speed and depends on the precisionrequired.
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| 9. |
- Rydblom, Staffan, 1975-, et al.
(författare)
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Particle Measurement Volume and Light Intensity in a Shadowgraph Imaging System
- 2018
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Ingår i: IST 2018 - IEEE International Conference on Imaging Systems and Techniques, Proceedings. - : IEEE. - 9781538666289
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Konferensbidrag (refereegranskat)abstract
- A method is sought to find the measurement volume of an optical instrument for particle measurement is sought. The study shows that the measurement volume depends on a combination of the optical homogeneity of the illumination light and the camera system. The result from a mix of illumination cases and positions shows that, if the true size and the background brightness are known, the measurement volume can be determined with an average precision of four percent using adual term exponential fit. Using a lens with lower magnification increases the measurement volume since both the field of viewand the depth of field increase. However, a larger field of view increases the required amount of light as well as the sensitivity to other optical errors.
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| 10. |
- Vilar, Cristian, et al.
(författare)
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Evaluation of embedded camera systems for autonomous wheelchairs
- 2019
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Ingår i: VEHITS 2019 - Proceedings of the 5th International Conference on Vehicle Technology and Intelligent Transport Systems. - : SciTePress. - 9789897583742 ; , s. 76-85
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Konferensbidrag (refereegranskat)abstract
- Autonomously driving Power Wheelchairs (PWCs) are valuable tools to enhance the life quality of their users. In order to enable truly autonomous PWCs, camera systems are essential. Image processing enables the development of applications for both autonomous driving and obstacle avoidance. This paper explores the challenges that arise when selecting a suitable embedded camera system for these applications. Our analysis is based on a comparison of two well-known camera principles, Stereo-Cameras (STCs) and Time-of-Flight (ToF) cameras, using the standard deviation of the ground plane at various lighting conditions as a key quality measure. In addition, we also consider other metrics related to both the image processing task and the embedded system constraints. We believe that this assessment is valuable when choosing between using STC or ToF cameras for PWCs.
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